1. Field of the Invention
The present invention relates to a centrifuge rotor for an evacuated centrifuge instrument and, in particular, to a rotor having a projection of a predetermined weight mounted to the rotor at a predetermined position thereon so as to be separable from the rotor at a predetermined rotor speed without causing the rotor to leave its drive mount.
2. Description of the Prior Art
A centrifuge instrument is a device adapted to expose a liquid sample to a centrifugal force field. The sample is disposed in a suitable container which is itself carried in a rotor member that is rotationally mounted within the centrifuge. The rotor is adapted to be driven to an extremely high rotational speed, often in excess of fifty thousand revolutions per minute, to generate the centrifugal force field.
The rotor is a relatively massive member fabricated of a high strength material such as titanium. To reduce the power requirements of the drive the centrifuge has an evacuable chamber in which the rotor is spun. The evacuated chamber minimizes the effects of windage (i.e., air friction) on the rotor.
Due to the high energy imparted to a massive member such as a rotor when the same is rotated at the extremely high rotational speed generated in a centrifuge, control of rotor speed is especially important. Extreme care must be exercised in order to maintain the rotational speed of the rotor under its burst speed. Burst speed is the speed at which the rotor will disintegrate and fly apart.
Rotor speed is typically controlled through the use of electronic networks associated with the electronic speed control arrangement for the centrifuge. In addition, prior art systems are available which attempt to limit rotor speed through the use of mechanical expedients. Generally speaking, such expedients include structural members attached to the rotor which become disassociated from the rotor in response to excessive rotor speed.
Exemplary of such a system is that shown in U.S. Pat. No. 3,961,745 (Wright). In this patent a breakable safety linkage is mounted to the rotor and arranged to fracture when the rotor reaches a predetermined rotational speed. When the safety linkage breaks the rotor becomes unbalanced, resulting in a shut-down of the centrifuge, usually manifested by an interruption of motive energy from the centrifuge drive. Other examples of devices generally similar in principle are disclosed in U.S. Pat. No. 3,990,633 (Stahl et al.) and U.S. Pat. No. 4,568,325 (Cheng et al.). Both of these patents disclose breakable members attached to the underside of the rotor. The members fracture when a predetermined rotor speed is reached thereby to isolate the rotor from its drive connection, thus causing the rotor to leave the drive.
In all of these mechanical arrangements, however, the effect of the mechanical fracture of the members is to unbalance the rotor and cause the same to leave its mounting to the drive. The rotor then physically displaces within the chamber in a random, unpredictable manner. As a result the cover of the rotor could become separated therefrom, perhaps spilling the samples on the interior of the instrument. Further, the rotor could be severely damaged, necessitating its replacement. Either or both of these consequences is perceived as disadvantageous.
In view of the foregoing it is believed to be desirable to provide a mechanical expedient whereby rotor overspeed may be prevented yet at the same time effect such control without the deleterious effect of causing the rotor to dismount from its drive connection.